This invention relates generally to the art of digital-to-analog converters (DAC), and more specifically concerns a DAC which is capable of processing a sign magnitude or ones compliment binary coded input.
There are two basic categories of conventional digital-to-analog converters: (1) a regular or straight DAC, which uses a DC reference voltage; and (2) a multiplying DAC, (MDAC) which uses an AC or DC reference voltage. Both the straight DAC and MDAC, however, are limited in the types of coded input they can process. Basically, there are five different binary codes: binary, offset binary, twos complement, ones complement, and sign magnitude. The conventional DACS are capable of processing straight binary, offset binary, and twos complement coded inputs, but are not capable of processing either sign magnitude or ones complement coded inputs. Both the sign magnitude and the ones complement coded inputs, however, are advantageous in many situations, because they are well adapted to generate symmetrical waveforms. Such binary inputs are potentially especially useful with MDACS for generating waveforms for modulated waveform synthesis applications, such as a graphic display. In order to take advantage of this capability, sign switches have been used at the output of conventional MDACS when the input is a sign magnitude code. However, this arrangement has a number of substantial operating disadvantages. Rather, extra circuitry or a computer is required to do a code conversion, which takes valuable time, and is expensive. There is no circuitry comparable to sign switches for one's complement, however, and thus, that input is not used at all.
Therefore, it is an object of the present invention to provide a DAC which overcomes one or more of the problems of the prior art noted above.
It is another object of the present invention to provide such a DAC which is capable of directly processing sign magnitude or ones complement coded inputs.
It is a further object of the present invention to provide such a DAC which constructed by modifying, in minimal fashion, a conventional digital-to-analog converter.
It is an additional object of the present invention to provide such a DAC which processes a sign magnitude or one's complement coded input substantially as quickly as other coded inputs.
It is yet another object of the present invention to provide such a DAC which processes sign magnitude/ones complement coded inputs without converting them to another input.